S2 Sci WA1

• Forces acting between two objects that are in physical contact with each other are called contact forces

  (eg friction, elastic force)
• friction is a force that opposes motion between 2 surfaces in contact (eg walking, writing w/ pencil)
• elastic force will give a force in the opposite direction when stretched or compressed
• non-contact forces act without touching each other (eg gravitational force, magnetic force)
• magnetic force is the force exerted between magnets and magnetic materials.
• gravitational force (weight) is a force that pulls object to the ground, preventing it from floating
• unlike poles attract each other.
• like poles repel each other
• mass is the amount of matter in an object
• The SI unit of mass is kilogram (kg) and the SI unit of force is Newton (N)
• The instrument to measure force is the extension spring balance and a spring.
• The extension spring balance works by stretching when there is a pulling force while the spring works by compressing when there is a pulling force.
• The quantity of matter (mass) does not change
• the weight of an object may change with its location
• when 2 or more objects interact, they exert force on one another. it results in the transfer of energy between objects
• a contact force occurs between two surfaces that are touching each other
• A non-contact force is a force that can act through empty space without any physical contact between the objects involved
• The types of changes are:

  -Move the stationary object

  -change speed of object

  -change direction of moving object

  -stop moving object

  -change object's shape
• A force applied on an object can cause a turning effect about a fixed point with little force
• Pressure is force per unit area, the effect of force acting on object
• the unit of pressure exerted depends on amount of force and area of contact.
• instruments to measure force are extension spring balance and spring
• extension spring: stretches when got pulling force
• spring/ compressing spring spring balance: compresses when there is a pushing force
• the amount/quantity of matter does not change, as the mass of a object remains the same
• the weight will change depending on how strong the gravity is on the planet (eg earth, moon)
• the smaller the contact, the higher the pressure

  the larger the contact, the lower the pressure
• daily uses of pressure are: injection, knife, etc
• the amount of pressure in a liquid depends on its depth
• at greater depths, the liquid pressure will be higher
• density= M/V (kg/m³)
• when layer of air particles pushes down on Earth's surface due to gravitational force, they exert pressure of approx. 1000000 Pa (pascal) at sea level
• when at height above sea level, fewer air particles push down on us
• a force applied causing an object to move in the same direction as force results in transfer of energy
• when energy is transferred, work is done through application of force
• transfer energy= amount of work done=joules (J)
• the conditions of work to be done are:

  -force applied

  -object move in same direction as force applied
• if the object is carried by a person walking, no work is done
• total energy in an isolated system remains constant
• energy is not created or destroyed, but transferred from one object to another, or converted from one form to another